The present invention is related to blown optical fiber. In particular, it is related to a method and apparatus for making a plurality of blown optical fiber insertions into a duct.
The apparatus and method for installing optical fiber in ducts by blowing the fiber through the duct are well-known to those of skill in the art and are described in U.S. Pat. Nos. 4,691,896 to Reeve et al.; 5,065,928 to Davey et al.; 5,165,662 to Jenkins; 5,181,271 to Jenkins; and 5,645,267 to Reeve et al. all of which are hereby incorporated by reference. Practical application of these fiber insertion methods revealed that as the number of fibers increased, the difficulty in gathering, directing, and metering the fibers for insertion were greatly amplified. Solutions to these difficulties involving the bundling of fibers (U.S. Pat. No. 4,997,256 to Sano et al.) into a coherent group resulted in reduced insertion distances and an overall reduction in the beneficial loose-tube cabling characteristics of blown fiber. Other solutions involving an optical path joint member (U.S. Pat. No. 5,781,678 to Sano et al.) have proved impractical due to the risk of damaging the fibers, both during the re-entry and insertion steps. It was obvious, however, that by using the current methods, the capacity for fiber density of the conduit was not fully realized.
By the present invention, a trap fitting was developed that permits a fiber or fiber bundle to be trapped in a duct while permitting subsequent blowing of a second fiber or fibers alongside and past the first trapped fiber. Until this invention, the only fitting on the market related to blown optical fiber was that which is manufactured by the John Guest Company. This fitting is not used for the insertion of blown optical fiber but is instead a fitting used to block the path of the duct or constrict around an object within the duct. The fitting is a pneumatic connector fitting that has a constricting diaphragm disposed within. When the fitting is twisted, the diaphragm constricts around an object in the duct and blocks the passageway through the duct. Such a fitting would not be suitable for use in the present invention because there is no way to subsequently blow a second group of fibers alongside the trapped fiber and through the duct because the duct is blocked.
By the present invention, a method and apparatus have been developed that permit a plurality of insertions of optical fiber or fibers into a duct while minimizing the risk of optical fiber breakage. The method employs an apparatus comprising a trap fitting that is mounted onto a duct. The trap fitting comprises a fitting mounted onto the duct downstream of a blow head. There is a passageway through a wall of the fitting and a cylindrical sleeve fixed to the exterior of the fitting over the passageway. A plunger is mounted in the cylindrical sleeve. The plunger is used to trap a first fiber against the wall of the fitting while leaving a suitable pathway for a second fiber to be blown through the trap fitting and into and through the duct to a terminal.
A new method for making a plurality of blown optical fiber insertions into a duct is presented wherein at least one fiber is installed in a duct through to a terminal. The fiber is then trapped in place. At least one second fiber is then blown alongside the first fiber and through the duct to a terminal. The method may be repeated any number of times to deploy the number of optical fibers desired.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be obtained by means of instrumentalities in combinations particularly pointed out in the appended claims.